Articles you may be interested inOn the sputtering yield of molecular ions J. Vac. Sci. Technol. A 3, 1913(1985; 10.1116/1.572944Sputtering yields of electrochemically deposited metal and metal oxide thin films Most of the published ion sputtering yield values are based on experimental techniques which do not correlate well with the ion sputtering process commonly used with surface analysis instrumentation. A need exists for ion sputtering yield measurements collected under the same conditions which will be used in practice. We have measured ion sputtering yields on several sputter-deposited metal films using the Auger electron spectroscopy "breakthrough" depth profile method, whereby characteristic Auger electron transitions for the thin film and the substrate are monitored while the thin film is being sputtered away. Rutherford backscattering spectrometry is used to measure the density of the films and a scanning stylus profilometer is used to measure the depth of the resulting sputter craters. The thin metal films exhibit a sputtering rate depth dependency, i.e., the sputtering decreases with the amount of material removed. It was shown that this phenomenon is related to surface roughening due to the directionality of the ion sputtering process. Reduction of the topographic effects with a significant improvement in depth resolution is demonstrated by continuously rotating the sample during ion bombardment.
There are two fundamental considerations in preparing samples for electron probe microanalysis (EPMA). The first one may seem obvious, but we often find it is overlooked. That is, the sample analyzed should be representative of the population from which it comes. The second is a direct result of the assumptions in the calculations used to convert x-ray intensity ratios, between the sample and standard, to concentrations. Samples originate from a wide range of sources. During their journey to being excited under the electron beam for the production of x rays there are many possibilities for sample alteration. Handling can contaminate samples by adding extraneous matter. In preparation, the various abrasives used in sizing the sample by sawing, grinding and polishing can embed themselves. The most accurate composition of a contaminated sample is, at best, not representative of the original sample; it is misleading. Our laboratory performs EPMA analysis on customer submitted samples and prepares over 250 different calibration standards including pure elements, compounds, alloys, glasses and minerals. This large variety of samples does not lend itself to mass production techniques, including automatic polishing. Our manual preparation techniques are designed individually for each sample. The use of automated preparation equipment does not lend itself to this environment, and is not included in this manuscript. The final step in quantitative electron probe microanalysis is the conversion of x-ray intensities ratios, known as the “k-ratios,” to composition (in mass fraction or atomic percent) and/or film thickness. Of the many assumptions made in the ZAF (where these letters stand for atomic number, absorption and fluorescence) corrections the localized geometry between the sample and electron beam, or takeoff angle, must be accurately known. Small angular errors can lead to significant errors in the final results. The sample preparation technique then becomes very important, and, under certain conditions, may even be the limiting factor in the analytical uncertainty budget. This paper considers preparing samples to get known geometries. It will not address the analysis of samples with irregular, unprepared surfaces or unknown geometries.
We describe the use of a wide-area (38 crrr'] electron beam as a heat source to interdiffuse 4OO-Athick sputter-deposited titanium films into 3-6-11 cm ( 1(0) n-type silicon wafers. Isochronal exposures of 30 s with electron beam of current densities greater than 250 mA/cm z reduced the as-deposited sheet resistance by a factor of 10, while exposures at halfthis current caused the sheet resistance to increase by a factor of 2.5. Compositional depth profiles obtained from a combination of ion beam sputtering and Auger electron spectroscopy show that this resistivity increase is caused by diffusion of oxygen into the titanium film induced by the electron beam heating. At exposures to beam intensities sufficient to induce complete silicide formation, oxygen is segregated at the surface by the advancing silicon. We conclude that the silicide self-cleanses itself of oxygen during formation. Silicides are attractive materials for both interconnections and contacts for very large scale integrated (VLSI) devices fabricated in silicon because oftheir low resistivities (as compared to highly doped polysilicon), their compatability with processing at high temperatures, and their controllable Schottky ohmic contact formation. I Of particular interest is titanium disilicide because its low resistivity (-15f-l11 cm) at room temperature) lies below that of pure Ti (42 f-l11 ern], thus offering a lower contact resistance than pure Ti. Additionally, TiSi z yields, as do most refractory metal silicides, barrier heights of nearly the same magnitude on both n-and p-type silicon.Silicides are generally created by one of two methods: (i) codeposition (via physical or chemical vapor deposition) of the constituent materials, usually requiring a subsequent high-temperature ( > 800 "C] annealing step to form the stoichiometric silicide, or (ii) deposition of the metallic film followed by a lower temperature (-600 "C)alloying heat treatment which interdiffuses the silicon and metal species to form the silicide. When a silicide is formed by interdiffusion of a deposited metal film on silicon, a more atomically clean silicide/silicon interface often results , thereby minimizing contamination-induced contact resistance variations. The heat source typically used in batch processing is a furnace. Alternative heat sources include scanned 50-100-f-lm-diam continuous laser and electron beams,z and exposure to the radiation from lOO-f-ls arc discharges in argon.' An advantage of electron beam driven alloying over laser-formed silicide layers is that the high optical reflectivity of most metals is not a factor. Hence an additional film above the metal is not required to increase energy coupling as in Ref. 2.The wide-area (38 cm Z ) source used in this work allows for rapid silicide formation in a single wafer in-line system. Prior to our present work a pulsed electron beam 1 in. in diameter was used to form MoSi z from molybdenum-silicon layered structure using a 25-J glow discharge electron beam of 1 f-lS duration propagating in lO-s Torr helium."...
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